SAN JUAN, Puerto Rico – An autopsy has found that a Guantanamo Bay prisoner who died in September took an overdose of medication in an apparent suicide, a U.S. official said Thursday.

Adnan Latif, who was found unconscious in his cell in a disciplinary wing of the prison at the U.S. base in Cuba, took an overdose of psychiatric medication, according to a senior Defense Department official.

The official said it had not yet been determined how Latif, who was from Yemen and had a history of mental illness and clashes with guards, managed to collect enough medication for a fatal dose. Investigators are looking into whether he hoarded pills to take all at once.

The autopsy results have not yet been officially released and the case remains the subject of an investigation by the Naval Criminal Investigative Service.

The U.S. military does not intend to disclose the results of the autopsy or discuss the case in further detail until after Latif’s remains are returned to his country, said Army Col. Greg Julian, a spokesman for the U.S. military’s Miami-based Southern Command, which has jurisdiction over Guantanamo. The remains are at the Ramstein Air Base in Germany.

His death was the seventh suicide at the prison, where the United States now holds 166 men. The deaths of two other prisoners were determined to be from natural causes.

The finding of suicide in the Latif case was first reported by the website Truthout, followed by The New York Times.

David Remes, an attorney for Latif, said he is skeptical of the military’s conclusion and said it would be difficult for the prisoner to accumulate enough medication to commit suicide because he was frequently searched and monitored inside the prison.